We would like to decrease the cost and increase the pertinence of studies of transplantation and immuno-suppression in dogs by making generally available standard pairs of donors and recipients of relatively known degrees of histocompatability or incompatability. To this end we would like to continue our several lines of closely bred beagles and to continue our studies of typing and selecting our breeding pairs and our exportable donor-recipient pairs on the basis of the major histocompatibility antigens that are detected on the lymphocytes of peripheral blood by cytotoxic alloimmune sera. When experiments in mice have shown methods for avoiding graft versus host disease in recipients of allogeneic marrow, we would like to evaluate their clinical potential in dogs of known histocompatibility, enhancing, and blocking factors in the control of growth of tumors trasmittable to members of our colony.